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Re: copy partition from a remote server

On Saturday 09 April 2005 00:32, Alex Malinovich wrote:
>On Sat, 2005-04-09 at 05:59 +0200, Frederic Guillet wrote:
>> Hi,
>> i want to run a daily back-up of an entire HD (160GO) remotely.
>> Do you know any tool that can perform this on an incremental
>> basis?
>rsync. That's almost EXACTLY what it's made for in the first place.
>It'll compare the checksums for remote files to local files and only
>transfer changes. (Meaning that if you've only changed 1MB worth of
> data in your 160GB HD, it'll only transfer 1MB of data +
> communication overhead.)

rsync works great, but it does have an achilles heel not everyone is 
aware of.  It works by compareing the local files checksum on a block 
of data with the checksum of the same block on the remote machine.  I 
they match, the remote machine is sent after the next block, and that 
block is copied locally from the real file to a temp file, beaucoup 
faster than the net copy.  When it reaches the end of the file, the 
local file is deleted, and the temp copy is renamed in its place.

Now, do you see the achilles heel?  You need scratchpad space at least 
as large as the largest file you are rsyncing.  If you have files 
that are multigigabyte, like some dvd images then it needs that same 
amount of scratchpad space on the target drive.  In other words, its 
time to build a bigger raid when that one gets up around 80-85% full.

Cheers, Gene
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Copyright 2005 by Maurice Eugene Heskett, all rights reserved.

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